In the first two papers of this series1we were able to show that a fat-splitting enzyme is present regularly in the urine of dogs. We presented the following observations as evidence that the fat-splitting enzyme is of pancreatic origin: 1. Injection of methacholine (Mecholyl) and secretin in dogs increases the amount of the fat-splitting enzyme in the urine. 2. Removal of the pancreas causes an immediate disappearance of the enzyme in the urine. 3. Ligation of the pancreatic ducts leads to a marked rise in the excreted amount of the enzyme followed slowly by a decrease to rather low values. 4. Ligation of the ducts followed by pancreatectomy causes an immediate disappearance of the high values of the enzyme in the urine. From these findings we concluded that the fat-splitting enzyme in the urine is identical with the pancreatic lipase. Lipase has also been detected regularly in the